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Old 5th April 2013, 03:29 AM   #1
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Default SuperPensils Not Doing It

I finished my SuperPensil build and while I love the Mark Audio A12P drivers I am not reaching frequencies below 55/60. That seems a bit off for a cabinet that size.

I am looking into the Bob Brines plans for the A12P in a MLTL.

Any thoughts? Recommendations? Things to try?

Thanks!

-Ron
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Old 5th April 2013, 03:55 AM   #2
xrk971 is offline xrk971  United States
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Ron,
Based on how big this box is and how low the fs of the A12 is, I would imagine that it should have no problem reaching 50 Hz. At the risk of offending the designers of the Pensil - but no offense is intended - all I can suggest is that I think that the vent does not have enough resistance to "pull" the tuning frequency low enough. If I apply my "Accidental MLTL Design" to this box, I get a longer vent length than just the thickness of the front baffle. Using WinISD: for a 40 in tall x 10.5 in wide x 14-7/8 in deep box (approx 104 liters volume) with a 2.0 in tall x 10.5 in wide vent, if I set the tuning frequency at 46 Hz, the vent length should be 2.55 in. This may be something you can easily try - make a 2.55 in x 10.5 in piece of stiff cardboard, or foam core board and tape that to the top lip of the vent to make a shelf vent. See if that improves the bass response. Very easy to do and reversible - you have nothing to lose. This should impose a little more resistance and improve the bass extension. A 0.75 in long vent would indicate a tuning freq of only 53 Hz according to WinISD. And if the lip is radiused, the freq is even higher due to lower resistance to air flow.

Accidental MLTL Technique

Last edited by xrk971; 5th April 2013 at 04:02 AM.
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Old 5th April 2013, 04:33 AM   #3
zman01 is offline zman01  Bangladesh
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Ron,

Have you played around with stuffing?

Are your drivers broken in?
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Old 5th April 2013, 04:40 AM   #4
mp9 is offline mp9  United States
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Ron, i would've guessed a stuffing problem, not enough fill, type of fill? Did you also line the walls with felt or such before the stuffing?

Let us know how you make out with Bob B's MLTL, seems interesting enough.

I'm not exactly clear on what a MLTL does differently then Resonant Air Coupler (Pencil), i.e., aside from physical size does one or the other yield higher efficiency, less extension, impedance differences...

- xrk971, Curious, can you run that WinISD program for 52.35L 35.5"x9"x10" standard Pencil design?
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Old 5th April 2013, 05:21 AM   #5
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Quote:
Originally Posted by mp9 View Post
I'm not exactly clear on what a MLTL does differently then Resonant Air Coupler (Pencil),
Pensil is an ML-TL.

dave
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Old 5th April 2013, 06:00 AM   #6
mp9 is offline mp9  United States
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Originally Posted by planet10 View Post
Pensil is an ML-TL.

dave
Ok like i said, confused. Frugal-phile box library says: "Mark Audio Pensil Series (complete set) Resonant Air Couplers updated 10-june-11" Frugal-phile | Box Library / Mark Audio

Pensil's and Bob's design (obviously i can't see the innards and he hasn't posted the box plan), look like a simple vented box, one slot loaded the other with a tube.
I'm not getting where the simple rectangle equates to a Mass Loaded-Transmission Line aspect of the two designs? two designs?
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Old 5th April 2013, 06:13 AM   #7
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Quote:
Originally Posted by RonVinyl View Post
I am not reaching frequencies below 55/60. That seems a bit off for a cabinet that size.
You didn't stuff the entire box by any chance? cogitech did that with his A10.2 Pencils and complained about the poor bass performance. When he removed some of the stuffing, the missing low bass emerged.

jeff
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Old 5th April 2013, 09:42 AM   #8
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by mp9 View Post
Ok like i said, confused. Frugal-phile box library says: "Mark Audio Pensil Series (complete set) Resonant Air Couplers updated 10-june-11" Frugal-phile | Box Library / Mark Audio

Pensil's and Bob's design (obviously i can't see the innards and he hasn't posted the box plan), look like a simple vented box, one slot loaded the other with a tube.
I'm not getting where the simple rectangle equates to a Mass Loaded-Transmission Line aspect of the two designs? two designs?
It has nothing to do with shape of vent but fact that vent serves to constrict the opening which would otherwise be fully open cross sectional area for a quarter wave tube. The constriction makes the resonant freq of the quarter wave tube act as if it was longer giving a lower resonant freq. Analogous to how adding mass to tips of tuning fork will bring its quarter wave freq down. So a vent makes it "mass loaded". A mass loaded TL is close to a bass reflex cabinet but elongated, if you collapse aspect ratio back to a classic golden ratio box, the mass loaded operation goes away and you go back to bass reflex. You can read more about this at Quarter Wavelength Loudspeaker Design
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Old 5th April 2013, 09:44 AM   #9
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by vinylkid58 View Post
You didn't stuff the entire box by any chance? cogitech did that with his A10.2 Pencils and complained about the poor bass performance. When he removed some of the stuffing, the missing low bass emerged.

jeff
Yes, +1 on this, make sure you follow stuffing plan. But typically no more than top 2/3 of pipe should be stuffed or 26 in down from top and the less you stuff, the more boomy the bass. If you stuff all the way and stuff densely, it becomes aperiodic and you get no bass enhancement.
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Old 5th April 2013, 12:24 PM   #10
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The pensils are not designed to extract the maximum possible extension from the drive unit. If that is what you want, then you need a different enclosure. I did such a box for a friend in Scotland; it's not been released on-line, nor will it be since I know Bob is doing a similar one, and I try not to cover the same turf. The pensils are a specific alignment tuned to provide pro-audio style broadband gain to the mid 50Hz regions that self-corrects for step-loss in most practical situations, while the box is stuffed throughout like a regular TL, providing a near-flat impedance load and linear drive unit deflection. This is a part of the design; however, as is made clear on the pdf's, a removable back to the enclosures is recommended to allow the damping to be adjusted to suit amplifier output impedance, room response and personal preference.

The A12P, excellent unit though it is, cannot be tuned quite as low as the original A12 in a vented box, be it an MLTL, BR or whatever. Mark traded off a little bottom-end extension for a couple of extra dB efficiency, greater HF extension and lower HD. Personally, I think this was a wise choice since the current model is significantly superior to the original in all areas but outright LF extension.
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